A New Twist on Turbo

by Amanda Phillips On May 2, 2007

Integrating electronic systems in every new truck is something that is happening more frequently, so it shouldn't be a complete surprise that turbocharger technology is advancing in this direction as well. To many medium-duty fleet maintenance managers, it is also new. According to Zack Ellison, director of customer technical support and industrial OEM support with Cummins, most technicians and managers have not encountered this kind of technology before.

"It's sort of a new world for maintenance people as far as turbos are concerned because they have never in the past had to worry about electronic fault codes for turbochargers, but today they do," Ellison says.

He adds that the electronically actuated turbocharger technology is on all of their medium-duty 2007 engines. It has what he calls a 'coolant-cooled bearing housing', with the center section of the turbocharger essentially cooled by engine coolant.

Ellison says this helps to reduce the turbocharger bearing temperatures, which is good for the life of the turbocharger.

"Maintenance managers need to understand that if you do a good job changing oil and using good engine oil filters, that actually takes care of the turbocharger," Ellison says. He also adds that part of the maintenance equation includes using quality multi-viscosity oil such as 15W-40 and a quality filter, just as it is also very important for technicians to follow maintenance manual procedures from the manufacturer.

Ellison explains that the turbocharger is actually the first component receiving oil filtered by the oil filter. "An oil line runs directly to the bearing," he says, "so there isn't any lag at start up and it feeds good oil to the bearings during shutdown."

Because the turbocharger is of an electronically actuated variable geometry (VG) variety, there will inevitably be the need for troubleshooting because of the electronic fault codes related to the operation and the actuation of the unit.

Cummins provides 'troubleshooting trees' or detailed information for technicians to follow in order to pinpoint problems based on fault codes.

"In some cases, they could get a fault code that could be related to the turbocharger operation, and go to the troubleshooting trees that give them step-by-step instructions to find where the problem is with that turbocharger," says Ellison.

'DIFFERENT' CAN BE GOOD

"It's a little bit different, but the benefits of the electronic controlled variable geometry turbocharger are pretty spectacular," he says.

Another aspect to this technology is better driveability, according to Ellison. That is when the turbocharger "spools up" or gets up to speed very quickly to provide engine boost levels almost as quickly as the throttle pedal is depressed.

The turbocharger also has the capability to perform as an exhaust brake to give the engine the maximum exhaust back pressure to help slow down the vehicle. Ellison says that this capability is built in to every electronically controlled VG turbocharger. Cummins no longer allows the addition of external exhaust brakes, which is a change from the past. It is also a major cost-savings, and saves the operator installation fees that could run anywhere from $700 to $1000. All of this is achieved with electronic technology, without affecting engine durability or reliability.

TROUBLE-FREE EFFICIENCY

"The turbocharger is actually one of the most important components for improving engine efficiency," Ellison says. He adds that because of engine efficiency, the amount of energy recovered from the exhaust via the turbocharger is also related to fuel economy.

"It's important when a turbocharger spools up quickly and maintains accurate boost levels throughout the engine RPM range. All of that goes to improve fuel economy," he says.

"Combined with the electronically controlled VG turbocharger and other improvements we made for '07 in the mid-range product line, it has enabled us to increase fuel economy by a few percentage points," Ellison continues.

Ellison says that fuel economy is not completely due to the turbocharger, but from a combination of the electronic controls and fuel injection.

"It's pretty much a trouble-free system," Ellison says. "For people that are familiar with the medium duty engines, the only thing that will catch them a little bit by surprise is the electronic VG actuator."

USING 'ELECTRONIC DISCIPLINE'

If the technician is observing fault codes, there are troubleshooting trees to follow. Of the two or three turbochargers that Ellison knows that needed to be escalated beyond the technician, he found out that the service request was because the technician incorrectly followed the 'troubleshooting tree,' or a consecutive order of steps to follow for turbocharger repair.

Technicians and dealers are also able to access the troubleshooting trees in an electronic manual called QuickServe Online. This is a Web-based program designed for communicating online troubleshooting techniques.

"Working with this new generation turbocharger is a bit different," Ellison says, "it takes a little more electronic discipline, but it's a quantum leap in turbocharger technology."

VTG TECHNOLOGY

The 2007 BorgWarner Turbocharger has been developed with variable turbine geometry (VTG) technology to provide boost control at all engine speeds, according to application engineer Adam Reinke with BorgWarner Turbo Systems. Using a traditional turbocharger package, Reinke says, this technology includes moveable guide vanes in the turbine housing to direct the speed and flow where the exhaust gases hit the turbine wheel.

He adds that the vanes are controlled by an electronic actuator mounted on the turbocharger. The vanes are moved from a fully open position, which makes the size of the turbine larger and allows more flow through it, to a fully closed position.

When fully closed, Reinke says, the flow is decreased and causes exhaust gas to accelerate through the turbine.

TURBO-CHARGED VERSATILITY

"There are two conditions you can look at for why a VTG is used," says Reinke. "At low engine speed and low load, there's not a lot of exhaust energy produced by the engine. If you close the vanes, you're maximizing the energy that's available because it accelerates the exhaust gas across the turbine wheel, which allows you to increase the boost pressure at those lower speeds. This reduces turbo lag, a common component of turbocharged engines."

An additional benefit, according to Reinke, is that there's an increase in exhaust back pressure by closing the vanes. "This helps drive exhaust gas recirculation, which lowers emissions output of the engines," he says.

Reinke also adds that under high-engine speed and high-load conditions there is a large amount of exhaust energy. During that time, the vanes can be opened to limit the boost and speed of the turbocharger. In turn, this will limit the boost that the turbocharger is delivering to the engine, which helps overall durability of the engine and turbocharger.

A combination of the vane mechanism is factored in to how the turbocharger helps meet emission targets.

"It can act like a small turbo, or it can act like a large turbo; it can accomplish both of those tasks in one package," Reinke says. "This allows for the flexibility to control it with electronic adjustment based on the driver's needs."

CHANGES IN 2007

For 2007, Reinke says that there are various improvements which increase the "robustness" of the turbocharger. The rotating components of the turbocharger are high-speed balanced, a process that spins the turbocharger at real-world turbo speeds, and records and corrects the balance level.

Reinke adds that the balancing process reduces the occurrence of instability at high turbo speeds.

"The bearing system has also been redesigned for increased durability," he says.

The VTG has also been updated to a new 'rollerless' design as well, according to Reinke, which features less moving parts and reduces the chance of binding or sticking in the mechanism.

"From an applications standpoint, you've got a lot of small-moving parts and a high-temperature environment. Reducing friction and increasing the corrosion-resistance is going to make a more durable part," says Reinke.

"A lot of validation effort and fine-tuning is needed to get everything to work right and survive in the field," he says. "All of the changes have come from lessons learned from previous field experience and during the development of the new turbocharger. These lessons applied to the 2007 turbo highlight the latest technology."

TURBO RELIABILITY

The VTG linkage in the turbocharger connects the actuator to the VTG mechanism, according to Reinke, and is developed with a ball-joint linkage. This reduces friction and increases the corrosion resistance of the linkage.

Reinke says that the linkage is an external part to the system that is often exposed to the salt spray and a changing engine environment.

But Reinke says that continuous validation testing on the turbochargers will improve performance and durability on the final product. He says that the development from concept to production takes about three years, but the validation process typically takes about two years to complete.

"A combination of technology improvements and lessons learned have improved the turbocharger system from previous generations," says Reinke.

"VTG technologies have been available for a few years now, and BorgWarner's technology highlights a more robust and durable product for 2007."